The present invention relates to devices for assembling motor-vehicle bodies or sub-assemblies thereof. The invention is applicable to devices for assembling vehicles of any type, such as cars, light or heavy trucks or the like. In particular, the invention relates to devices for assembling structures made of pressed sheet metal by electric spot welding. However, the invention is also applicable to any other assembling system, such as by adhesive, as well as to any other material, such as plastic or composite materials.
More in detail, the invention relates to devices for assembling motor-vehicle bodies or subassemblies thereof, of the known type comprising:
an assembling station, provided with programmable assembling means, PA1 conveyor means, for carrying at least a portion of the structure to be assembled into the assembling station as well as for taking the structure after that it has been assembled out of the assembling station, PA1 at least one pair of locating and locking gates arranged on two opposite sides of the assembling station, provided with locating and locking devices for holding the component elements of the structure to be assembled in the proper assembling position, while the assembling operation is being carried out, said gates being movable towards and away from each other, between a spaced inoperative condition, in which said locating and locking devices are disengaged from the structure to be assembled, and a closed operative condition, in which said locating and locking devices are able to engage the structure to be assembled. PA1 a) each locating and locking gate is an independent unit, having a base portion movable in the assembling station and adapted to be rigidly locked to a fixed structure of the station in the above mentioned operative condition of the gate, and an active portion, carrying the above mentioned locating and locking devices, which extends from said base portion and is not connected directly to said fixed structure of the station in the said operative condition of the gate, so as to remain free to undergo micro-deflections along a direction transverse relative to the longitudinal direction of the station, due to variations of the transverse dimension of the structure to be assembled with respect to a theoretical predetermined dimension, PA1 b) between said active portion of each locating and locking gate and said fixed structure there are interposed sensor means adapted to detect the micro-displacement of said active portion with respect to said fixed structure due to said micro-deflection, at a predetermined distance from the area where the base portion of the gate is locked to the fixed structure, PA1 c) said device further comprises means for processing the signals coming from said sensor means and for calculating the displacement of the various area of the active portion of each locating and locking gate, as a function of the distance from said locked area, as well as for calculating, if desired, the force exchanged between each gate and the structure to be assembled.
Assembling devices of the above indicated type are well known and have been used for a long time. For example, the Applicant has been producing and marketing a flexible welding system identified under the trademark "ROBOGATE" for years, whose basic concept has been shown originally in U.S. Pat. No. 4,256,957 and parallel German patent No. 28 10 822 and which gave rise with the time to a number of subsequent improvements and variants which also have formed the subject of respective patents of the Applicant. The ROBOGATE system has indeed determined a break-through in the welding technique of motor-vehicle bodies which was generally used until the end of the seventies and has replaced the apparatus previously used with many car manufacturers all around the world. In a basic version of the system, it comprises two or more pairs of locating gates which are rapidly interchangeable at the welding station and are adapted to operate on respective types of bodies. The system is able to operate on bodies even very different from each other, so that a same line can be used for producing different models. A further advantage of the ROBOGATE system lies in that it can be adapted by relatively simple and rapid operation, and hence with very reduced investments, to the production of a new body model. Another advantage lies in that a uniform quality of all the models of a same type on which the system operates is assured.
The present invention can be applied both to a flexible station using many pairs of locating gates, and also to a "rigid" station, comprising a single pair of locating gates which are for operating on a single body model.
In the case of the above described known devices, the assembling means are constituted by programmable robots provided with heads for electric spot welding. However, as already indicated, the present invention can be applied whatever is the technology used for connecting the various parts of the structure together.
A further feature of the above described known device, lies in that the structure to be welded reaches the welding station after it has been loosely assembled. Devices of the same type are also known, in which only a portion of the structure to be welded is caused to enter in to the welding station, the remaining parts which are necessary for forming the complete structure to be welded being fed separately to the welding station and connected there with each other. The present invention may be identically applied also to devices of this type.
Following the above mentioned patents relating to the basic version of the ROBOGATE system, the Applicant has filed further patents relating to various improvements and variants of this system. A recent improvement has formed the subject of European patent application EP-A-0 642 878 which has been mentioned above already. In this document a welding station is disclosed which has a much less complicated, light and more flexible structure with respect to the prior embodiments of the ROBOGATE system. In the most conventional solutions, the above mentioned locating gates are slidably guided, in order to render them rapidly interchangeable at the welding station with the gates provided for a different type of body to be welded, on overhead guides directed parallel to the direction of the conveyor line at the welding station, which requires the provision of heavy fixed supporting frameworks. These frameworks, beyond contributing greatly to the cost and the bulk of the welding station, also render difficult for the welding robots to find the necessary space in order to operate on the body to be welded. In the solution described in European patent application EP-A-0 642 878, each locating gate is movable independently from the other gates since it is provided with a lower self-propelled cart guided on a rail provided along the floor of the welding station. Therefore, the locating gates do not require any longer the provision of longitudinal overhead guides extending throughout the whole length between their working position at the welding station and their waiting position spaced from the welding station, so that also the provision of the heavy and bulky supporting framework, usually constituted by gantry-like structures connected with each other longitudinally, which was necessary in the classic ROBOGATE plants is no longer needed. Thus, the space available for the welding robots is greatly increased, which also enables, if desired, the number of robots to be increased in order to obtain an increase of the number of welding spots carried out within a predetermined time. The robot may access much more easily to all the regions of the body to be welded in order to carry out proper welding. Furthermore, since each locating gate is movable independently from the other gates, the pitch between each gate and the subsequent gate along the line is free and variable, which provides a greater flexibility in design and installation of the plant. Finally, the installation itself of the plant is of a more reduced cost with respect to that of more conventional plants. This known system, which has been marketed by the Applicant under the trademark "OPEN-ROBOGATE" has been disclosed in European paten application EP-A-0 642 878 which has been mentioned above with reference to a first embodiment, which relates to the case in which all the components of the structure to be welded are carried to the welding station from said conveyor line, in a condition already preassembled or anyhow with the various elements supported separately from each other, but at positions close to the final assembling position. The further European patent application No. 97830456.6 has proposed a new version of the "OPEN-ROBOGATE" system in which the conveyor line each time feeds only a portion of the structure to be welded (typically the floor panel) to the welding station, whereas the body sides are formed directly on the locating gates, which then attend to bring them into engagement with the floor panel when the gates are moved into their closed operative position. Obviously, in this second version, the so-called toy-tabbing stations which were provided in the most conventional solutions upstream of the welding station, in order to loosely assemble the bodies before welding, are eliminated. Furthermore, the conveyor line becomes simpler and less expensive with respect also to the embodiment shown in European patent application EP-A-0 642 878, since the complete structure of the body is formed starting from its single components only at the welding station and not upstream thereof.
The present invention provides a further improvement of the "OPEN-ROBOGATE" system both with reference to the variant shown in European patent application EP-A-0 642 878, and the variant forming the subject of European patent application No. 97830456.6. Moreover, the invention is applicable both to a station of the above indicated type which is flexible, i.e. comprising many pairs of locating gates rapidly interchangeable with each other in order to adapt themselves to various types of body to be welded, as well as to a rigid station, comprising a single pair of locating gates dedicated to a single body model.
Technical Problem to be Solved
A problem which has been encountered in the past with welding stations of the above described known type, lies in that the assembled structure has a width, i.e. a dimension along a direction transverse relative to the longitudinal direction of the welding station, which not always corresponds to a predetermined theoretical dimension. Even the most modern and sophisticated embodiments do not prevent variations with respect to the predetermined width which at minimum are in the order of some millimeters.
With ROBOGATE stations of conventional type, in which the locating gates are guided by means of rigid supporting frameworks, when the structure to be welded is locked between the locating gates, it is compelled to assume a theoretical configuration. Therefore, when welding is completed and the locating gates are opened leaving the welded structure free, the latter may be subject to a sort of relaxation which takes it to a condition not corresponding to the desired theoretical one. If one wishes to improve the precision of the system by accurately studying the deformation to which the welded structure is subjected, he must provide complicated detection systems using strain gauges, or subsequent offline measurement evaluation which are expensive and involve troublesome test operations.